My most often used lenses are the 40-150mm and the Sigma 30mm. (I also have the 14mm which has the same thread as the Sigma, and the 14-42mm, which is used less often.)

I have two choices to make:

1. Get a 58mm filter and a 46mm->58mm step-up, or two filters?

2. Which brand? The B + W and the Sigma filters are priced similarly, a notch above the Hoya and twice the price of Tiffen.

Opinions most welcome!

i have a Kenko Zeta, and i must say that it was quite expensive. i don't know about your budget, but it might not be worth buying two filters. I would start with a 58mm diameter filter, because it will be easier to buy an adapter for 46mm. you could go the other way, but i don't know if it wouldn't cut the edges of the frame.

for the 46mm lens you will most likely not be able to use a hood with the 58mm filter on. if you buy a model that has a thread on the outside maybe you can get a threaded round hood. that will also make it easier to adjust the filter. i have to adjust the filter and then mount the hood, as i am using the 14-42mm kit part.